You are given 100K cash to invest, and are limited to EITHER QQQQ's or Nasdaq-100 Futures.

Your always-correct crystal ball says that it is one month before a new bull market in the NASDAQ, and you want to get positioned. Bull market should last 2+ years.

Which one? Why? Which gives you more bang-for-the-buck?

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Your question doesn't make any sense at all. If you got your always correct crystal ball then, as it has been mentioned, it's a no brainer, go for futures as you get greater leverage and preferential tax treatment if you're a US tax payer.